Probably your AB list is text. You can check with the ISTEXT() function.
Copy an empty cell.
Select your AB column data
EditPaste special, check Add
Ok now?

--
Kind regards,

Niek Otten
Microsoft MVP - Excel

"NS" wrote in message
...
I am setting a following formula:

=IF(AB187,"A",IF(AB184,"B+",IF(AB178,"B",IF(AB1 72,"C",IF(AB1<73,"F",0)))))

for grades of student.

It gives me error. For example. If student got 87 he should have B+
according to formula. However, excel gives me "A" instead of B+.

Please help